Heretofore, an acrylic resin has been widely used in the fields of molding materials, coating compositions, adhesives, etc., in view of its good durability and environmental friendliness, among other things.
An acrylic adhesive is used for bonding by polymerizing and curing an acrylic monomer or oligomer utilizing an organic peroxide and a reducing agent which decomposes the organic peroxide to generate radicals, which function as a polymerization initiator.
A combination of an organic peroxide with a reducing agent is generally called “a curing initiator system”. Further, a “two-pack type acrylic adhesive” is an acrylic adhesive comprising two agents of (A) a composition containing an organic peroxide and (B) a composition containing a reducing agent, and it is also called a two liquid chief agent type adhesive since the two agents (A) and (B) are in the form of a liquid in most cases.
The two-pack type acrylic adhesive is used for a method of mixing the above two agents (A) and (B) immediately before use and applying the mixture to an object to be bonded, and a method of applying the above (A) to a surface of one object to be bonded and applying the above (B) on a surface of the other object to be bonded, and contacting both surfaces.
Cumene hydroperoxide, which can be used for (A), is an organic hydroperoxide having a hydroperoxide group, and is commonly used by virtue of a long half-life at room temperature.
The reducing agent, which can be used for (B) is roughly classified as a mixture of an ethylene thiourea derivative with a metallic soap or a mixture of an ethylene thiourea derivative with a metal chelate compound. An adhesive using such a reducing agent, which is cured at a high speed at room temperature as compared with an epoxy adhesive, has been developed (Patent Documents 1 to 4).
However, even with such a reducing agent, no adhesive which is cured in seconds at room temperature while maintaining adhesive characteristics ultimately required, has been realized. Accordingly, a temporary fixing jig is used for the purpose of preventing misalignment in the bonding position or falling, during the period from bonding till fixing by curing, at present. When using an acrylic adhesive at the present state of the art, a lot of temporary fixing jigs must be used in the bonding site. Therefore, for example, productivity in production of steel plate products cannot be improved, thereby preventing the cost reduction.
An adhesive which can bond an object at a determined position without use of a temporarily fixing jig, which overcomes the above problem, has been strongly desired.    Patent Document 1: JP-A-52-018478    Patent Document 2: U.K. Patent No. GB 715382    Patent Document 3: U.S. Pat. No. 3,591,438    Patent Document 4: U.S. Pat. No. 3,625,930